Unidentified assailants opened fire outside a city hall in the northern Mexico border state of Sonora on Thursday, killing two men and a woman.
The attack took place outside the city hall in the Gulf of California port of Guaymas. The state prosecutors office urged residents to avoid the downtown area. Police, marines and National Guard units responded to the attack.
Sonora has been the scene of bloody turf battles between several cartels, but it was unclear if Thursday's shooting was related to that.
The shooting comes one day after state authorities said they found 14 clandestine graves near Miguel Aleman, a town north of Guaymas.
State prosecutors say the burial pits contained bones, some burned, and decomposing bodies, but said they cannot yet determine the number of victims.Sonora has been the scene of drug gang turf battles thought to involve factions of the Sinaloa Cartel, allies of the Jalisco cartel and a gang allied with fugitive drug lord Rafael Caro Quintero.